It has long been usual, in particular in the manufacture of miniaturized semiconductor components, to use masks provided with structures to produce structures of very filigree design in a photolithographic manner on substrates (wafers) for electronic circuits. In this connection, high demands are made on the masks, in particular on the useable structures formed on them. However, this also relates to their purity and protection against adhering particles is thus desired.
Since the sizes of the structures to be formed on the respective substrates have been made smaller and smaller in the more recent past, the corresponding demands on purity and freedom from defects of masks during use have increased. Masks have thus been provided with so-called pellicles. Pellicles are protective elements for the mask structure. They consist of a frame and of a membrane optically transparent in the photolithographic application. The pellicle is then connected with material continuity to the mask using adhesive at a lower side of the frame which is disposed opposite the side of the pellicle at which the membrane is connected to the frame. The mask structure is thus protected by the pellicle and its membrane. Since the membrane is arranged at a spacing from the structured surface of the mask, particles adhering to the membrane can be imaged out of the focal length during the exposure procedure and not on the respective substrate surface so that no exposure errors are caused by particles.
It has, however, been found that defects can occur directly at the mask structure during use. However, they cannot be eliminated or corrected due to the pellicle arranged in front of them. A temporary removal of pellicles is required for this purpose.
Such a removal has previously almost only been carried out manually. In this connection, the respective mask is heated so that the adhesive used softens and then a pellicle can be removed from the mask by hand by an operator. It is obvious that this represents an unsatisfactory state and the required purity demands can thus not be observed to the required degree.
Mounts for handling are formed at the frames, and indeed at their radially outer edges. The pellicles used are, however, neither normed nor standardized so that pellicles can have different dimensions as regards e.g. the geometrical design and the dimensioning. Frames can have different heights so that different spacings of the membrane of pellicles to the mask surface can occur. This also applies to the mounts. Different adhesives are used for the connection with material continuity which can accordingly also have properties which differ from one another, that is, also different detachment behavior.
A large number of these differences could previously be taken into account by an operator by the manual operation. In addition to the already mentioned purity concerns, however, it was not possible to avoid incorrect actions of operators sufficiently so that damage to or even the destruction of cost-intensive masks occurred which then had to be replaced by newly prepared masks.